In the electronics industry it is often desirable to cover or coat an existing refractory metal surface with a brazable or solderable surface. Applications for such a procedure, include but are not limited to, I/O pads, wire bond pads, C4's (Controlled Collapse Chip Connection) and, seal bands, to name a few.
Many methods are available and practiced in the industry to cover or coat an existing refractory metal surface with a brazable or solderable surface. The most commonly used approach for treating refractory metal surfaces in the microelectronic packaging business is to employ electroplating or electroless-plating of pure or substantially pure Ni (nickel) film.
Nickel is generally the metal of choice for plating refractory metals because it can be made to bond well with any of the refractory metals. In addition, Ni possesses good wetting characteristics for subsequent bonding processes, such as brazing or soldering, and it has excellent corrosion characteristics.
U.S. Pat. No. 4,664,942 (Park), is one prior art process for covering surface areas of tungsten or molybdenum with nickel to make the surface brazable or solderable. Park teaches the process of nickel metallization of a ceramic device pre-metallized with Mo or W. In a nickel workboat having a nickel cover, an alumina crucible having Ni/NH.sub.4 I/Al.sub.2 O.sub.3 particulate mixture is placed. Within this nickel workboat a ceramic device premetallized with molybdenum or tungsten is placed along with a nickel screen. This assembly is then exposed to high temperature to complete the nickel metallization of the premetallized ceramic device.
However, this invention teaches a new process for electroless deposition of a Ni or Ni alloys on a refractory metal surface. It is a CVD process which is performed in a dry environment and at a high temperature using an iodide, preferably an iodide salt, such as, for example, CuI, as the active reagent.